Method of preparing metal chalcogenide nanoparticles and method of producing light absorption layer thin film based thereon

ABSTRACT

Disclosed are a single-source precursor for synthesizing metal chalcogenide nanoparticles for producing a light absorption layer of solar cells comprising a Group VI element linked as a ligand to any one metal selected from the group consisting of copper (Cu), zinc (Zn) and tin (Sn), metal chalcogenide nanoparticles produced by heat-treating at least one type of the single-source precursor, a method of preparing the same, a thin film produced using the same and a method of producing the thin film.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2014-0157951 filed on Nov. 13, 2014 with the Korean IntellectualProperty Office, the disclosure of which is herein incorporated byreference in its entirety.

TECHNICAL FIELD

The present invention relates to metal chalcogenide nanoparticles forproducing a CZTS-based solar cell light absorption layer, a method ofpreparing the same, a CZTS-based solar cell light absorption layerproduced using the nanoparticles and a method of producing a solar cell.

BACKGROUND ART

Solar cells have been manufactured using a light absorption layer formedat high cost and silicon (Si) as a semiconductor material since an earlystage of development. To more economically manufacture industriallyapplicable solar cells, structures of thin film solar cells, using aninexpensive light absorbing material such as copper indium gallium(di)selenide (CIGS) or Cu(In, Ga)(S, Se)₂, have been developed. SuchCIGS-based solar cells typically include a rear electrode layer, ann-type junction part, and a p-type light absorption layer. Solar cellsincluding such CIGS layers have a power conversion efficiency of greaterthan 19%. However, in spite of potential for CIGS-based thin film solarcells, costs and insufficient supply of indium (In) are main obstaclesto wide applicability and availability of thin film solar cells usingCIGS-based light absorption layers. Thus, there is an urgent need todevelop solar cells using In-free or In-less low-cost universalelements.

Accordingly, as an alternative to the CIGS-based light absorption layer,CZTS(Cu₂ZnSn(S,Se)₄-based solar cells including copper (Cu), zinc (Zn),tin (Sn), sulfur (S), or selenium (Se), which is an extremely cheapelement, have recently received much attention. Advantageously, CZTS hasa direct band gap of about 1.0 eV to about 1.5 eV and an absorptioncoefficient of 10⁴ cm⁻¹ or more, reserves thereof are relatively high,and CZTS uses Sn and Zn, which are inexpensive.

CZTS hetero junction PV batteries were first reported in 1996, butCZTS-based solar cells are technologically less advanced than CIGS-basedsolar cells and photoelectric efficiency of CZTS-based solar cells is10% or less which is much lower than that of CIGS-based solar cells.Thin films of CZTS are prepared by sputtering, hybrid sputtering, pulsedlaser deposition, spray pyrolysis, electro-deposition/thermalsulfurization, e-beam processing, Cu/Zn/Sn/thermal sulfurization, and asol-gel method.

Meanwhile, PCT/US/2010-035792 discloses formation of a thin film throughheat-treatment of a substrate using ink including CZTS/Se nanoparticles.Generally, when a CZTS thin film is formed with CZTS/Se nanoparticles,it is difficult to enlarge crystal size in the subsequent process offorming a thin film due to previously formed small crystals. As such,when each grain is small, interfaces are extended, causing electron lossat interfaces. Accordingly, efficiency is inevitably deteriorated.

Accordingly, nanoparticles used in a thin film should include Cu, Zn andSn, and should not be a CZTS crystal type. However, disadvantageously,in a case where only metal nanoparticles composed of a single metalelement are used, the metal nanoparticles are easily oxidized and asubsequent additional process for removing oxygen using excess Se andhigh temperature is required.

Therefore, there is an increasing need for technologies associated withmetal chalcogenide nanoparticles which maintain an overall homogenousmetal composition and are produced by a simplified process.

DISCLOSURE Technical Problem

Therefore, the present invention has been made to solve the above andother technical problems that have yet to be resolved.

As a result of a variety of extensive and intensive studies andexperiments, the present inventors developed a single-source precursorincluding a Group VI element linked as a ligand to any one metalselected from the group consisting of copper (Cu), zinc (Zn) and tin(Sn), as a single-source precursor to synthesize metal chalcogenidenanoparticles for producing a light absorption layer of solar cells, andfound that, in this case, metal chalcogenide nanoparticles which have anoverall uniform composition and high economic efficiency can be producedwithout incorporating an additional Group VI element source. The presentinvention has been completed based on these findings.

Technical Solution

In accordance with one aspect of the present invention, provided is asingle-source precursor for synthesizing metal chalcogenidenanoparticles for producing a light absorption layer of solar cellswhich includes a Group VI element linked as a ligand to any one metalselected from the group consisting of copper (Cu), zinc (Zn) and tin(Sn).

When the Group VI element is linked as a ligand to the metal describedabove, an additional Group VI element source is unnecessary, thusadvantageously reducing process costs and simplifying the overallprocess.

The single-source precursor for synthesizing metal chalcogenidenanoparticles for producing a light absorption layer of solar cellsaccording to the present invention is specifically a copper (Cu)-ligandcomplex, a tin (Sn)-ligand complex, or a zinc (Zn)-ligand complex.

In a specific embodiment, the ligand is not limited so long as it isuseful as a Group VI element source and for example includes one or moreselected from the following compounds:

wherein R represents an alkyl group having n or more carbons (n≧1), forexample, a methyl group, an ethyl group or a propyl group.

In the single-source precursor, the number of ligands bound to the metalis not particularly limited and may for example be 2 or 4, and the kindof ligand bound to one metal may be one or more.

The present invention provides metal chalcogenide nanoparticles producedby heat-treating one or more types of the single-source precursor.

Herein, “heat-treating one or more types of the single-source precursor”means that only one type of single-source precursors that can bevariably prepared may be heat-treated or two or more types of thesingle-source precursors may be heat-treated, and “chalcogenide” means asubstance containing a Group VI element, for example, sulfur (S) and/orselenium (Se).

Specifically, the metal chalcogenide nanoparticles can be prepared byheat-treating one type of the single-source precursor and the metalchalcogenide nanoparticles thus prepared may, for example, be copper(Cu)-containing chalcogenide nanoparticles, tin (Sn)-containingchalcogenide nanoparticles, or zinc (Zn)-containing chalcogenidenanoparticles.

Specifically, the copper (Cu)-containing chalcogenide nanoparticles maybe CuS and/or CuSe, the tin (Sn)-containing chalcogenide nanoparticlesmay be SnS and/or SnSe, and the zinc (Zn)-containing chalcogenidenanoparticles may be ZnS and/or ZnSe.

In a specific embodiment, the metal chalcogenide nanoparticles can beprepared by heat-treating two types of single-source precursors and themetal chalcogenide nanoparticles thus prepared may, for example, becopper (Cu)-tin (Sn)-containing chalcogenide nanoparticles, copper(Cu)-zinc (Zn)-containing chalcogenide nanoparticles, or tin (Sn)-zinc(Zn)-containing chalcogenide nanoparticles.

Specifically, the copper (Cu)-tin (Sn)-containing chalcogenidenanoparticles may be Cu_(a)SnS_(b) (0.1≦a≦1.0, 0.1≦b≦10.0), and/orCu_(s)SnSe_(t) (0.1≦s≦10.0, 0.1≦t≦10.0), the copper (Cu)-zinc(Zn)-containing chalcogenide nanoparticles may be Cu_(c)ZnS_(d)(0.1≦c≦10.0, 0.1≦d≦10.0), and/or Cu_(u)ZnSe_(v) (0.1≦u≦10.0,0.1≦v≦10.0), or the tin (Sn)-zinc (Zn)-containing chalcogenidenanoparticles may be Sn_(e)ZnS_(f) (0.1≦e≦10.0, 0.1≦f≦10.0) and/orSn_(x)ZnSe_(y) (0.1≦x≦10.0, 0.1≦y≦10.0).

In a specific embodiment, the metal chalcogenide nanoparticles can beprepared by heat-treating three types of single-source precursors andthe metal chalcogenide nanoparticles thus prepared may, for example, becopper (Cu)-tin (Sn)-zinc (Zn)-containing chalcogenide nanoparticles.

Specifically, the copper (Cu)-tin (Sn)-zinc (Zn)-containing chalcogenidenanoparticles may be Cu_(g)Zn_(h)SnS_(i) (1.0≦g≦10.0, 0.5≦h≦3.0,0.1≦i≦10.0,) and/or Cu_(p)Zn_(q)SnSe_(r) (1.0≦p≦10.0, 0.5≦q≦3.0,0.1≦r≦10.0).

In addition, the metal chalcogenide nanoparticles according to thepresent invention may be composite nanoparticles including two or morechalcogenides.

In a specific embodiment, the composite nanoparticles including twochalcogenides may, for example, be composite nanoparticles composed ofcopper (Cu)-containing chalcogenide and tin (Sn)-containingchalcogenide, composite nanoparticles composed of copper (Cu)-containingchalcogenide and zinc (Zn)-containing chalcogenide, or compositenanoparticles composed of tin (Sn)-containing chalcogenide and zinc(Zn)-containing chalcogenide and may also be composite nanoparticlescomposed of copper (Cu)-tin (Sn)-containing chalcogenide and zinc(Zn)-containing chalcogenide, composite nanoparticles composed of copper(Cu)-zinc (Zn)-containing chalcogenide and tin (Sn)-containingchalcogenide, or composite nanoparticles composed of tin (Sn)-zinc(Zn)-containing chalcogenide and copper (Cu)-containing chalcogenide.

More preferably, the copper (Cu)-tin (Sn)-zinc (Zn)-containingchalcogenide nanoparticles or the composite nanoparticles includingcopper (Cu), tin (Sn) and zinc (Zn) according to the present inventiondo not require addition of an additional metal source and can thusexhibit improved uniformity because each nanoparticle includes all ofcopper (Cu), tin (Sn) and zinc (Zn).

In addition, the composite nanoparticles have a core-shell structure, incontrast to general nanoparticles. Specifically, the compositenanoparticles including copper (Cu)-containing chalcogenide and tin(Sn)-containing chalcogenide may be core-shell structured nanoparticlesincluding a core including copper (Cu)-containing chalcogenide and ashell including tin (Sn)-containing chalcogenide, the compositenanoparticles including copper (Cu)-containing chalcogenide and zinc(Zn)-containing chalcogenide may be core-shell structured nanoparticlesincluding a core including copper (Cu)-containing chalcogenide and ashell including zinc (Zn)-containing chalcogenide, the compositenanoparticles including tin (Sn)-containing chalcogenide and zinc(Zn)-containing chalcogenide may be core-shell structured nanoparticlesincluding a core including tin (Sn)-containing chalcogenide and a shellincluding zinc (Zn)-containing chalcogenide, the composite nanoparticlesincluding copper (Cu)-tin (Sn)-containing chalcogenide and zinc(Zn)-containing chalcogenide may be core-shell structured nanoparticlesincluding a core including copper (Cu)-tin (Sn)-containing chalcogenideand a shell including zinc (Zn)-containing chalcogenide, the compositenanoparticles including copper (Cu)-zinc (Zn)-containing chalcogenideand tin (Sn)-containing chalcogenide may be core-shell structurednanoparticles including a core including copper (Cu)-zinc(Zn)-containing chalcogenide and a shell including tin (Sn)-containingchalcogenide, and the composite nanoparticles including tin (Sn)-zinc(Zn)-containing chalcogenide and copper (Cu)-containing chalcogenide maybe core-shell structured nanoparticles including a core including tin(Sn)-zinc (Zn) chalcogenide and a shell including copper (Cu)-containingchalcogenide. In this case, the core-shell structured nanoparticles mayhave a particle diameter of 2 nanometers to 200 nanometers.

The core-shell structured nanoparticles are stable against oxidizationso that formation of oxides can be minimized on grain surfaces andreactivity can thus be improved upon formation of thin films, becausecopper (Cu), tin (Sn) and zinc (Zn) metals are further homogeneouslymixed and the core including respective particles is protected by theshell including metal-containing chalcogenide.

Meanwhile, methods of preparing the metal chalcogenide nanoparticles canbe changed according to shape (structure) of the nanoparticles and thepresent invention provides methods of preparing metal chalcogenidenanoparticles depending on the structure thereof.

In an embodiment, the metal chalcogenide nanoparticles can be preparedby heat-treating a mixture including at least one type of single-sourceprecursor including a Group VI element linked as a ligand to any onemetal selected from the group consisting of copper (Cu), zinc (Zn) andtin (Sn).

By the method described above, copper (Cu)-containing chalcogenidenanoparticles, tin (Sn)-containing chalcogenide nanoparticles, or zinc(Zn)-containing chalcogenide nanoparticles, and copper (Cu)-tin(Sn)-containing chalcogenide nanoparticles, copper (Cu)-zinc(Zn)-containing chalcogenide nanoparticles, tin (Sn)-zinc(Zn)-containing chalcogenide nanoparticles, or copper (Cu)-tin (Sn)-zinc(Zn)-containing chalcogenide nanoparticles or the like can be prepared.

In another embodiment, a method of preparing the metal chalcogenidenanoparticles may include:

(a) heat-treating a mixture including at least one type of single-sourceprecursor including a Group VI element linked as a ligand to any onemetal selected from the group consisting of copper (Cu), zinc (Zn) andtin (Sn); and

(b) adding, to the heat-treated mixture, a mixture including at leastone type of single-source precursor including a Group VI element linkedas a ligand to any one selected from metals, among the copper (Cu), zinc(Zn) and tin (Sn), not selected in step (a) and heat-treating theresulting mixture.

In addition, the method may further include, after step (b), adding amixture including at least one type of single-source precursor includinga Group VI element linked as a ligand to any one selected from metals,among the copper (Cu), zinc (Zn) and tin (Sn), not selected in steps (a)and (b), and heat-treating the resulting mixture.

By the method described above, composite nanoparticles including copper(Cu)-containing chalcogenide and tin (Sn)-containing chalcogenide,composite nanoparticles including copper (Cu)-containing chalcogenideand zinc (Zn)-containing chalcogenide, or composite nanoparticlesincluding tin (Sn)-containing chalcogenide and zinc (Zn)-containingchalcogenide can be produced. In addition composite nanoparticlesincluding copper (Cu)-tin (Sn)-containing chalcogenide and zinc(Zn)-containing chalcogenide, composite nanoparticles including copper(Cu)-zinc (Zn)-containing chalcogenide and tin (Sn)-containingchalcogenide, or composite nanoparticles including tin (Sn)-zinc(Zn)-containing chalcogenide and copper (Cu)-containing chalcogenide canbe produced. In this case, the composite nanoparticles may be core-shellstructured nanoparticles, as described above.

In the method of preparing metal chalcogenide nanoparticles, theheat-treatment is carried out at a temperature of 50 to 300° C. Whenheat-treatment is conducted at a temperature lower than 50° C., ligandscannot be sufficiently decomposed and it is difficult to synthesize thedesired nanoparticles according to the present invention, and whenheat-treatment is conducted at a temperature higher than 300° C.,disadvantageously, desired nanoparticles are decomposed or other phasesas well as desired nanoparticles may be formed.

The method of preparing metal chalcogenide nanoparticles according tothe present invention involves simply heat-treating a single-sourceprecursor including a Group VI element linked as a ligand to a metal,thus not requiring an additional Group VI element source, a cappingagent, a reducing agent or the like to offer low process costs and asimple process.

In addition, the present invention provides an ink composition forpreparing a light absorption layer including one or more types of themetal chalcogenide nanoparticles dispersed in a solvent and a method ofproducing a thin film using the metal chalcogenide nanoparticles.

As mentioned above, “Including one or more types of the metalchalcogenide nanoparticles according to the present invention” meansincluding one or more of all types of metal chalcogenide nanoparticlesthat can be prepared according to the present invention.

In order to form a CZTS thin film of the present invention, the inkcomposition should include copper (Cu), zinc (Zn) and tin (Sn).Accordingly, the ink composition may, for example, be composed of acombination of at least one of copper (Cu), zinc (Zn) and tin (Sn), suchas a combination of copper (Cu)-containing chalcogenide nanoparticlesand tin (Sn)-zinc (Zn)-containing chalcogenide nanoparticles, acombination of copper (Cu)-tin (Sn)-containing chalcogenidenanoparticles and copper (Cu)-zinc (Zn)-containing chalcogenidenanoparticles, and a combination of copper (Cu)-tin (Sn)-zinc(Zn)-containing chalcogenide nanoparticles and copper (Cu)-tin(Sn)-containing chalcogenide nanoparticles.

In this case, the composition of metal chalcogenide nanoparticlesincluded in the ink composition may be Cu_(j)Zn_(k)Sn (1.0≦j≦4.0,0.5≦k≦2.0).

When the metal composition is not within the range, disadvantageously,secondary phases can be formed and solar cells cannot normally functionbecause the composition does not fall into a general composition ofCZTS.

In addition, the content of the Group VI element in metal chalcogenidenanoparticles included in the ink composition may be 0.5 to 4.0, withrespect to 1 mole of the total metal amount.

When the ratio of the Group VI element is not within the range and is,for example, lower than 0.5 moles, sufficient Group VI elements cannotbe supplied, films that are partially deficient in Group VI elements canbe formed and the films may be oxidized, and the ratio exceeds 4.0moles, thin films may non-uniformly grow due to non-uniform distributionof Group VI elements in the thin films and the Group VI sourceevaporates during heat treatment for producing thin films,disadvantageously causing excess pores to be created in final thinfilms.

Meanwhile, the method of producing a thin film using the metalchalcogenide nanoparticles according to the present invention includes:

(i) dispersing, in a solvent, one or more types of the metalchalcogenide nanoparticles according to the present invention to preparean ink;

(ii) coating a substrate provided with an electrode with the ink; and

(iii) drying the ink coated on the substrate provided with an electrode,and conducting heat treatment.

As such, when the thin film is produced using the metal chalcogenidenanoparticles according to the present invention, stable metalchalcogenide having no phase change can suppress formation of secondaryphases in the thin film and provide an overall uniform composition ofCu, Zn and Sn.

In a specific embodiment, the solvent of step (i) may be used withoutparticular limitation so long as it is a generally used organic solvent.The solvent may be an organic solvent selected from alkane, alkene,alkyne, aromatic, ketone, nitrile, ether, ester, organic halide,alcohol, amine, thiol, carboxylic acid, phosphine, phosphate, sulfoxideand amide, or a combination thereof.

Specifically, the alcohol solvent may be at least one mixed solventselected from ethanol, 1-propanol, 2-propanol, 1-pentanol, 2-pentanol,1-hexanol, 2-hexanol, 3-hexanol, heptanol, octanol, ethylene glycol(EG), diethylene glycol monoethyl ether (DEGMEE), ethylene glycolmonomethyl ether (EGMME), ethylene glycol monoethyl ether (EGMEE),ethylene glycol dimethyl ether (EGDME), ethylene glycol diethyl ether(EGDEE), ethylene glycol monopropyl ether (EGMPE), ethylene glycolmonobutyl ether (EGMBE), 2-methyl-1-propanol, cyclopentanol,cyclohexanol, propylene glycol propyl ether (PGPE), diethylene glycoldimethyl ether (DEGDME), 1,2-propanediol (1,2-PD), 1,3-propanediol(1,3-PD), 1,4-butanediol (1,4-BD), 1,3-butanediol (1,3-BD), α-terpineol,diethylene glycol (DEG), glycerol, 2-(ethylamino)ethanol,2-(methylamino)ethanol, and 2-amino-2-methyl-1-propanol.

The amine solvent may be at least one mixed solvent selected fromtriethylamine, dibutyl amine, dipropyl amine, butylamine, ethanolamine,diethylenetriamine (DETA), triethylenetetramine (TETA), triethanolamine,2-aminoethyl piperazine, 2-hydroxyethyl piperazine, dibutylamine,tris(2-aminoethyl)amine and hexylamine.

The thiol solvent may be at least one mixed solvent selected from1,2-ethanedithiol, pentanethiol, hexanethiol, and mercaptoethanol.

The alkane solvent may be at least one mixed solvent selected fromhexane, heptane and octane.

The aromatic solvent may be at least one mixed solvent selected fromtoluene, xylene, nitrobenzene and pyridine.

The organic halide solvent may be at least one mixed solvent selectedfrom chloroform, methylene chloride, tetrachloromethane, dichloroethane,and chlorobenzene.

The nitrile solvent may be acetonitrile.

The ketone solvent may be at least one mixed solvent selected fromacetone, cyclohexanone, cyclopentanone, and acetyl acetone.

The ether solvent may be at least one mixed solvent selected from ethylether, tetrahydrofuran and 1,4-dioxane.

The sulfoxide solvent may be at least one mixed solvent selected fromdimethyl sulfoxide (DMSO), and sulfolane.

The amide solvent may be at least one mixed solvent selected fromdimethyl formamide (DMF), and n-methyl-2-pyrrolidone (NMP).

The ester solvent may be at least one mixed solvent selected from ethyllactate, γ-butyrolactone, and ethyl acetoacetate.

The carboxylic acid solvent may be at least one mixed solvent selectedfrom propionic acid, hexanoic acid, meso-2,3-dimercaptosuccinic acid,thiolactic acid, and thioglycolic acid.

However, these solvents are given only as examples and the presentinvention is not limited thereto.

If necessary, an additive may be further added to prepare the ink instep (i).

The additive may, for example, include at least one selected from thegroup consisting of a dispersant, a surfactant, a polymer, a binder, acrosslinking agent, an emulsifying agent, an anti-foaming agent, adrying agent, a filler, a bulking agent, a thickening agent, a filmconditioning agent, an antioxidant, a fluidizer, a leveling agent and acorrosion inhibitor. In particular, the additive may include at leastone selected from the group consisting of polyvinylpyrrolidone (PVP),polyvinyl alcohol (PVA), Anti-terra 204, Anti-terra 205, ethylcellulose, and DispersBYK110.

For example, the method of forming the coating layer of step (ii) mayinclude one or more selected from the group consisting of wet coating,spray coating, spin-coating, doctor blade coating, contact printing, topfeed reverse printing, bottom feed reverse printing, nozzle feed reverseprinting, gravure printing, micro gravure printing, reverse microgravure printing, roller coating, slot die coating, capillary coating,inkjet-printing, jet deposition, and spray deposition.

The heat-treatment of step (iii) may be carried out in the presence of Sor Se. The method may optionally include selenization in order toprepare a solar cell thin film with a high density. The selenization maybe carried out through a variety of methods.

In the first example, the selenization may be carried out by dispersingS and/or Se in the form of a particle in a solvent together with themetal chalcogenide nanoparticles of step (i) to prepare an ink andconducting the heat treatment of step (iii).

In the second example, the selenization may be carried out by conductingthe heat treatment of step (iii) in the presence of S or Se. Morespecifically, the presence of S or Se can be achieved by supplying H₂Sor H₂Se gas or supplying Se or S gas through heating.

In the third example, the selenization may be carried out by, after step(ii), depositing S or Se on a thin film.

In addition, the present invention provides a thin film produced by themethod.

The thin film may have a thickness of 0.5 μm to 3.0 μm, morespecifically, 0.5 μm to 2.5 μm.

When the thickness of the thin film is less than 0.5 μm, desiredphotoelectric efficiency cannot be obtained due to insufficient densityand amount of the light absorption layer, and when the thickness of thethin film exceeds 3.0 μm, as movement distances of carriers increase, apossibility of leading to recombination is increased and deteriorationin efficiency thus occurs.

Furthermore, the present invention provides a thin film solar cellproduced using the thin film.

A method of producing the thin film solar cell is well-known to thoseskilled in the art and detailed explanation thereof is thus omitted.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is an SEM image of metal chalcogenide nanoparticles according toExample 1;

FIG. 2 is an XRD graph of metal chalcogenide nanoparticles according toExample 1;

FIG. 3 is an enlarged TEM image of metal chalcogenide nanoparticlesaccording to Example 1;

FIG. 4 is an SEM image of metal chalcogenide nanoparticles according toExample 4;

FIG. 5 is an XRD graph of metal chalcogenide nanoparticles according toExample 4;

FIG. 6 is an SEM image of metal chalcogenide nanoparticles according toExample 6;

FIG. 7 is an XRD graph of metal chalcogenide nanoparticles according toExample 6;

FIG. 8 is an EDX analysis table of the metal chalcogenide nanoparticlesaccording to Example 6;

FIG. 9 is an SEM image of a thin film produced in Example 7;

FIG. 10 is an XRD graph of the thin film produced in Example 7;

FIG. 11 is an SEM image of a thin film produced in Example 8;

FIG. 12 is an XRD graph of the thin film produced in Example 8;

FIG. 13 is an SEM image of a thin film produced in Example 9;

FIG. 14 is an XRD graph of the thin film produced in Example 9;

FIG. 15 is an SEM image of a thin film produced in Comparative Example4;

FIG. 16 is an XRD graph of the thin film produced in Comparative Example4;

FIG. 17 is an I-V graph of a solar cell produced from the thin filmproduced in Example 7;

FIG. 18 is an I-V graph of a solar cell produced from the thin filmproduced in Example 8;

FIG. 19 is an I-V graph of a solar cell produced from the thin filmproduced in Example 9; and

FIG. 20 is an I-V graph of a solar cell produced from the thin filmproduced in Comparative Example 4.

BEST MODE

Now, the present invention will be described in more detail withreference to the following examples. These examples are provided only toillustrate the present invention and should not be construed as limitingthe scope and spirit of the present invention.

EXAMPLE 1

Synthesis of Metal Chalcogenide Nanoparticles (Cu₂SnS₃/ZnS)

4 mmol of a Cu(CS₂NEt₂)₂ single source precursor and 2 mmol of aSn(CS₂NEt₂)₄ single source precursor were mixed with 20 mL of oleic acidand 180 mL of 1-octadecene. The mixture was heated to 160° C. andreacted for 1 hour to prepare Cu₂SnS₃ nanoparticles.

A dispersion of the Cu₂SnS₃ nanoparticles was centrifuged and washedthree times with 1-octadecene. The resulting substance was mixed with aZn(CS₂OEt)₂ single source precursor, followed by heating to 120° C. andreacting for 1 hour to prepare metal chalcogenide nanoparticlesincluding composite nanoparticles including a Cu₂SnS₃ phase and a ZnSphase, and Cu₂SnS₃—ZnS nanoparticles. The metal chalcogenidenanoparticles were purified by centrifugation.

The scanning electron microscope (SEM) image, XRD graph and transmissionelectron microscope (TEM) image of the formed metal chalcogenidenanoparticles are shown FIGS. 1 to 3.

As a result of XRD analysis, the particles are found to be present as acombination of a Cu₂SnS₃ crystal phase with a ZnS crystal phase, and ascan be seen from FIG. 3, the particles are present as compositenanoparticles including uniformly distributed Cu₂SnS₃ and ZnS phases, orCu₂SnS₃—ZnS structured nanoparticles.

EXAMPLE 2

Synthesis of Metal Chalcogenide Nanoparticles (Cu₂SnS₃/ZnS)

4 mmol of a Cu(CS₂NEt₂)₂ single source precursor and 2 mmol of aSn(CS₂NEt₂)₄ single source precursor were mixed with 20 mL of oleic acidand 180 mL of 1-octadecene. The mixture was heated to 160° C. andreacted for 1 hour to prepare Cu₂SnS₃ nanoparticles.

A dispersion of the Cu₂SnS₃ nanoparticles was centrifuged and washedthree times with 1-octadecene. The resulting substance was mixed with aZn(CS₂NEt₂)₂ single source precursor, followed by heating to 120° C. andreacting for 1 hour to prepare metal chalcogenide nanoparticlesincluding composite nanoparticles including a Cu₂SnS₃ phase and a ZnSphase, and Cu₂SnS₃—ZnS nanoparticles. The metal chalcogenidenanoparticles were purified by centrifugation.

EXAMPLE 3

Synthesis of Metal Chalcogenide Nanoparticles (Cu₂SnS₃)

4 mmol of a Cu(CS₂NEt₂)₂ single source precursor and 2 mmol of aSn(CS₂NEt₂)₄ single source precursor were mixed with 20 mL of oleic acidand 180 mL of 1-octadecene. The mixture was heated to 160° C. andreacted for 1 hour to prepare Cu₂SnS₃ nanoparticles. The Cu₂SnS₃nanoparticles were centrifuged.

EXAMPLE 4 Synthesis of Metal Chalcogenide Nanoparticles (ZnS)

4 mmol of a Zn(CS₂NEt₂)₂ single source precursor was mixed with 100 mLof xylene. The mixture was heated to 130° C. and reacted for 1 hour toprepare ZnS nanoparticles. The Cu₂SnS₃ nanoparticles were centrifuged.

The scanning electron microscope (SEM) image and XRD graph of the formedmetal chalcogenide nanoparticles are shown in FIGS. 4 and 5.

EXAMPLE 5 Synthesis of Metal Chalcogenide Nanoparticles (ZnS)

4 mmol of a Zn(CS₂OEt)₂ single source precursor was mixed with 100 mL ofxylene. The mixture was heated to 130° C. and reacted for 1 hour toprepare ZnS nanoparticles. The ZnS nanoparticles were centrifuged.

EXAMPLE 6

4 mmol of a Cu(CS₂NEt₂)₂ single source precursor, 2 mmol of aSn(CS₂NEt₂)₄ single source precursor and 2.4 mmol of a Zn(CS₂NEt₂)₂single source precursor were mixed with 20 mL of oleic acid and 180 mLof 1-octadecene. The mixture was heated to 160° C. and reacted for 1hour to prepare metal chalcogenide nanoparticles including compositenanoparticles including a Cu₂SnS₃ phase and a ZnS phase, and Cu₂SnS₃—ZnSnanoparticles. The metal chalcogenide nanoparticles were purified bycentrifugation.

The scanning electron microscope (SEM) image and XRD graph of the formedmetal chalcogenide nanoparticles are shown in FIGS. 6 and 7.

As a result of XRD analysis, the particles are found to be present as acombination of a Cu₂SnS₃ crystal phase with a ZnS crystal phase, and ascan be seen from FIG. 8, the Cu₂SnS₃ and ZnS phases are uniformlydistributed.

COMPARATIVE EXAMPLE 1 Synthesis of ZnS Particles

5 mmol of zinc nitrate and 10 mmol of Na₂S were dissolved in 50 ml ofwater, and the resulting aqueous zinc nitrate solution was addeddropwise to the aqueous Na₂S solution to synthesize ZnS. The formedparticles were purified by centrifugation.

COMPARATIVE EXAMPLE 2 Synthesis of CuS Particles

5 mmol of copper nitrate and 10 mmol of Na₂S were dissolved in 50 ml ofwater, and the resulting aqueous copper nitrate solution was addeddropwise to the aqueous Na₂S solution to synthesize CuS. The formedparticles were purified by centrifugation.

COMPARATIVE EXAMPLE 3 Synthesis of SnS Particles

5 mmol of tin chloride and 10 mmol of Na₂S were dissolved in 50 ml ofwater, and the resulting aqueous tin chloride solution was addeddropwise to the aqueous Na₂S solution to synthesize SnS. The formedparticles were purified by centrifugation.

EXAMPLE 7 Production of Thin Film

The Cu₂SnS₃—ZnS particles produced in Example 1 were dispersed in amixed solvent containing an alcohol-based solvent to prepare an ink andthe ink was coated on a glass substrate coated with molybdenum (Mo).After the coating film was dried, it was heated with a Se-depositedglass substrate to secure a Se atmosphere and rapid thermal annealing(RTA) was conducted at 575° C. to produce a CZTSSe-based thin film. Thescanning electron microscope (SEM) image and XRD graph of the producedthin film are shown in FIGS. 9 and 10.

EXAMPLE 8 Production of Thin Film

The Cu₂SnS₃ produced in Example 3 and ZnS particles produced in Example5 were dispersed in a mixed solvent containing an alcohol-based solventto prepare an ink and the ink was coated on a glass substrate coatedwith molybdenum (Mo). After the coating film was dried, it was heatedwith a Se-deposited glass substrate to secure a Se atmosphere and rapidthermal annealing (RTA) was conducted at 575° C. to produce aCZTSSe-based thin film. The scanning electron microscope (SEM) image andXRD graph of the produced thin film are shown in FIGS. 11 and 12.

EXAMPLE 9 Production of Thin Film

The Cu₂SnS₃—ZnS particles produced in Example 6 were dispersed in amixed solvent containing an alcohol-based solvent to prepare an ink andthe ink was coated on a glass substrate coated with molybdenum (Mo).After the coating film was dried, it was heated with a Se-depositedglass substrate to secure a Se atmosphere and rapid thermal annealing(RTA) was conducted at 575° C. to produce a CZTSSe-based thin film. Thescanning electron microscope (SEM) image and XRD graph of the producedthin film are shown in FIGS. 13 and 14.

COMPARATIVE EXAMPLE 4 Production of Thin Film

CuS, SnS and ZnS particles produced in Comparative Examples 1 to 3 weredispersed in a mixed solvent containing an alcohol-based solvent toprepare an ink and the ink was coated on a glass substrate coated withmolybdenum (Mo). After the coating film was dried, it was heated with aSe-deposited glass substrate to secure a Se atmosphere and rapid thermalannealing (RTA) was conducted at 575° C. to produce a CZTSSe-based thinfilm. The scanning electron microscope (SEM) image and XRD graph of theproduced thin film are shown in FIGS. 15 and 16.

TEST EXAMPLE 1 Production of Thin Film Solar Cell

The CZTSSe-based thin films produced in Examples 7 to 9 and ComparativeExample 4 were etched with a potassium cyanide (KCN) solution, a CdSlayer (thickness: 50 nm) was laminated by chemical bath deposition(CBD), a ZnO layer (thickness: 100 nm) and an Al-doped ZnO layer(thickness: 500 nm) were sequentially laminated by sputtering to producea thin film, and an aluminum (Al) electrode was formed on the thin filmto produce a thin film solar cell. The properties obtained from thesolar cells are shown in the following Table 1 and FIGS. 17 to 20.

TABLE 1 J_(sc) V_(oc) FF Photoelectric (mA/cm²) (V) (%) efficiency (%)Example 7 11.6 0.268 26.4 0.82 Example 8 26.8 0.290 41.3 3.2 Example 93.568 0.15 28.9 0.15 Comparative 1.36 0.2 24.68 0.1 Example 4

J_(sc) which is a parameter determining an efficiency of solar cellsshown in Table 1 means current density, V_(oc) means an open circuitvoltage measured at zero output current, photoelectric efficiency meansa ratio of cell power with respect to an energy amount of light incidentupon a solar cell panel, and fill factor (FF) means a value calculatedby dividing a value obtained by multiplying current density by voltageat a maximum power point by a value obtained by multiplying V_(oc) byJ_(sc).

As a result of testing, it can be seen that solar cells includingCZTSSe-based thin films produced in Examples 7 to 9 exhibit superiorcell characteristics, as compared to the solar cell including theCZTSSe-based thin film produced in Comparative Example 4.

In addition, the solar cell including the CZTSSe-based thin filmproduced in Example 8 exhibits superior cell characteristics such asJ_(sc), FF and photoelectric efficiency, as compared to the solar cellincluding the CZTSSe-based thin film produced in Example 9. Among metalchalcogenide nanoparticles according to the present invention, Cu—Sn—Zncomposite nanoparticles provide further superior cell characteristics.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

INDUSTRIAL APPLICABILITY

As apparent from the fore-going, the metal chalcogenide nanoparticlesaccording to the present invention for producing a light absorptionlayer of solar cells are produced by heat-treating at least one type ofsingle-source precursor including a Group VI element linked as a ligandto any one metal selected from the group consisting of copper (Cu), zinc(Zn) and tin (Sn), and can be produced only with a single source withoutincorporating an additional Group VI element source. Accordingly, thereis an advantage in terms of economic efficiency of particles and metalchalcogenide nanoparticles having no phase change are synthesized. Thinfilms produced from such metal chalcogenide nanoparticles canadvantageously minimize formation of secondary phases.

In particular, core-shell structured composite nanoparticles have astructure in which a core is protected by a shell includingmetal-containing chalcogenide, thereby being stable against oxidation,minimizing formation of oxides on particle surfaces and improvingreactivity during formation of thin films.

1. A single-source precursor for synthesizing metal chalcogenidenanoparticles for producing a light absorption layer of solar cellscomprising a Group VI element linked as a ligand to any one metalselected from the group consisting of copper (Cu), zinc (Zn) and tin(Sn).
 2. The single-source precursor according to claim 1, wherein thesingle-source precursor comprises a copper (Cu)-ligand complex, a tin(Sn)-ligand complex or a zinc (Zn)-ligand complex.
 3. The single-sourceprecursor according to claim 1, wherein the ligand comprises one or moreselected from the following:


4. Metal chalcogenide nanoparticles produced by heat-treating at leastone type of single-source precursor comprising the single-sourceprecursor according to claim
 1. 5. The metal chalcogenide nanoparticlesaccording to claim 4, wherein the metal chalcogenide nanoparticlescomprise copper (Cu)-containing chalcogenide nanoparticles, tin(Sn)-containing chalcogenide nanoparticles, or zinc (Zn)-containingchalcogenide nanoparticles.
 6. The metal chalcogenide nanoparticlesaccording to claim 4, wherein the metal chalcogenide nanoparticlescomprise copper (Cu)-tin (Sn)-containing chalcogenide nanoparticles,copper (Cu)-zinc (Zn)-containing chalcogenide nanoparticles, or tin(Sn)-zinc (Zn)-containing chalcogenide nanoparticles.
 7. The metalchalcogenide nanoparticles according to claim 4, wherein the metalchalcogenide nanoparticles comprise copper (Cu)-tin (Sn)-zinc(Zn)-containing chalcogenide nanoparticles.
 8. The metal chalcogenidenanoparticles according to claim 4, wherein the metal chalcogenidenanoparticles comprise composite nanoparticles comprising copper(Cu)-containing chalcogenide and tin (Sn)-containing chalcogenide, orcomposite nanoparticles comprising copper (Cu)-containing chalcogenideand zinc (Zn)-containing chalcogenide, or comprise compositenanoparticles comprising tin (Sn)-containing chalcogenide and zinc(Zn)-containing chalcogenide.
 9. The metal chalcogenide nanoparticlesaccording to claim 8, wherein the composite nanoparticles comprisingcopper (Cu)-containing chalcogenide and tin (Sn)-containing chalcogenideare core-shell structure nanoparticles comprising a core comprisingcopper (Cu)-containing chalcogenide and a shell comprising tin(Sn)-containing chalcogenide; the composite nanoparticles comprisingcopper (Cu)-containing chalcogenide and zinc (Zn)-containingchalcogenide are core-shell structure nanoparticles comprising a corecomprising copper (Cu)-containing chalcogenide and a shell comprisingzinc (Zn)-containing chalcogenide; and the composite nanoparticlescomprising tin (Sn)-containing chalcogenide and zinc (Zn)-containingchalcogenide are core-shell structure nanoparticles comprising a corecomprising tin (Sn)-containing chalcogenide and a shell comprising zinc(Zn)-containing chalcogenide.
 10. The metal chalcogenide nanoparticlesaccording to claim 4, wherein the metal chalcogenide nanoparticlescomprise composite nanoparticles comprising copper (Cu)-tin(Sn)-containing chalcogenide and zinc (Zn)-containing chalcogenide, orcomposite nanoparticles comprising copper (Cu)-zinc (Zn)-containingchalcogenide and tin (Sn)-containing chalcogenide, or compositenanoparticles comprising tin (Sn)-zinc (Zn)-containing chalcogenide andcopper (Cu)-containing chalcogenide.
 11. The metal chalcogenidenanoparticles according to claim 10, wherein the composite nanoparticlescomprising copper (Cu)-tin (Sn)-containing chalcogenide and zinc(Zn)-containing chalcogenide are core-shell structure nanoparticlescomprising a core comprising copper (Cu)-tin (Sn)-containingchalcogenide and a shell comprising zinc (Zn)-containing chalcogenide;the composite nanoparticles comprising copper (Cu)-zinc (Zn)-containingchalcogenide and tin (Sn)-containing chalcogenide are core-shellstructure nanoparticles comprising a core comprising copper (Cu)-zinc(Zn)-containing chalcogenide and a shell comprising tin (Sn)-containingchalcogenide; and the composite nanoparticles comprising tin (Sn)-zinc(Zn)-containing chalcogenide and copper (Cu)-containing chalcogenide arecore-shell structure nanoparticles comprising a core comprising tin(Sn)-zinc (Zn) chalcogenide and a shell comprising copper(Cu)-containing chalcogenide.
 12. A method of preparing the metalchalcogenide nanoparticles according to claim 4 comprising heat-treatingat least one type of single-source precursor comprising a Group VIelement linked as a ligand to any one metal selected from the groupconsisting of copper (Cu), zinc (Zn) and tin (Sn).
 13. A method ofpreparing the metal chalcogenide nanoparticles according to claim 4comprising: (a) heat-treating a mixture including at least one type ofsingle-source precursor including a Group VI element linked as a ligandto any one metal selected from the group consisting of copper (Cu), zinc(Zn) and tin (Sn); and (b) adding, to the heat-treated mixture, amixture including at least one type of single-source precursor includinga Group VI element linked as a ligand to any one selected from metals,among the copper (Cu), zinc (Zn) and tin (Sn), not selected in step (a),and heat-treating the resulting mixture.
 14. The method according toclaim 13, further comprising: after step (b), adding a mixture includingat least one type of single-source precursor including a Group VIelement linked as a ligand to any one selected from metals, among thecopper (Cu), zinc (Zn) and tin (Sn), not selected in steps (a) and (b),and heat-treating the resulting mixture.
 15. The method according toclaim 12, wherein the heat-treatment is carried out at a temperature of50 to 300° C.
 16. An ink composition comprising at least one type of themetal chalcogenide nanoparticles according to claim 4 dispersed in asolvent.
 17. The ink composition according to claim 16, wherein themetal chalcogenide nanoparticles comprised in the ink composition have acomposition of Cu_(j)Zn_(k)Sn (1.0≦j≦4.0, 0.5≦k≦2.0).
 18. The inkcomposition according to claim 16, wherein a molar ratio of the Group VIelement of the metal chalcogenide nanoparticles comprised in the inkcomposition is 0.5 to 4.0, with respect to 1 mole of the total metalamount.
 19. A method of producing a thin film using the metalchalcogenide nanoparticles according to claim 4 comprising: (i)dispersing, in a solvent, at least one type of the metal chalcogenidenanoparticles according to claim 4 to prepare an ink; (ii) coating asubstrate provided with an electrode with the ink; and (iii) drying theink coated on the substrate provided with an electrode, and conductingheat treatment.
 20. The method according to claim 19, wherein thesolvent of step (i) comprises at least one organic solvent selected fromthe group consisting of alkane, alkene, alkyne, aromatic, ketone,nitrile, ether, ester, organic halide, alcohol, amine, thiol, carboxylicacid, phosphine, phosphate, sulfoxide and amide.
 21. The methodaccording to claim 19, further comprising adding an additive to preparethe ink in step (i).
 22. The method according to claim 21, wherein theadditive comprises at least one selected from the group consisting ofpolyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), Anti-terra 204,Anti-terra 205, ethyl cellulose, and DispersBYK110.
 23. The methodaccording to claim 19, wherein the coating of step (ii) is carried outby wet coating, spray coating, doctor blade coating, or inkjet-printing.24. The method according to claim 19, wherein the heat-treatment of step(iii) is carried out in the presence of S or Se.
 25. The methodaccording to claim 24, wherein the presence of S or Se is carried out bysupplying H₂S or H₂Se gas or supplying Se or S gas through heating. 26.The method according to claim 19, further comprising supplying S or Seas a particle and supplying the same during heat-treating.
 27. Themethod according to claim 19, further comprising supplying S or Se on athin film by deposition.
 28. A thin film produced by the methodaccording to claim
 19. 29. A thin film solar cell produced using thethin film according to claim 28.